The present invention relates to a two-dimensional optical element array and a two-dimensional waveguide apparatus. Specifically, this invention relates to a two-dimensional optical element array with a high alignment precision of optical elements (optical fiber, lens, for example) on a substrate and a high long-term reliability, and a two-dimensional waveguide apparatus having high density and capacity and allowing the number of steps in packaging or connection to be reduced.
Recently, with the increased communications data capacity, a demand for an optical cross-connect switch technique that provides a higher throughput of communications data has increased. For example, there has been used an optical switch that is manufactured using the MEMS (micro-electro-mechanical-system) for conducting fine machining in a semiconductor process including silicon etching, which is used for micro-machining and the like. Additionally, with the increased demand for reliability, as well as the demand for the higher throughput, a surface-emitting laser enabling communications with high definition and stability has come into common use.
In such an optical switch or surface-emitting laser, an optical element array is used (optical fiber array, lens array, waveguide (PLC) array, semiconductor laser (LD) array, photo diode (PD) array, for example). In the description hereinafter, the xe2x80x9coptical fiber arrayxe2x80x9d is taken as an example of the optical element array. In consideration of requirements for increased throughput and space-saving, the optical fiber array is a so-called two-dimensional optical fiber array (occasionally abbreviated as 2DFA hereinafter) whose cross-section taken along a plane perpendicular to central axes of the aligned optical fibers has a two-dimensional (hierarchical) configuration.
For example, as shown in FIG. 16, there has been proposed a conventional two-dimensional optical fiber array 100 with a pitch in a thickness direction determined by controlling a thickness of a substrate 102 with V-shaped grooves with high precision, arranging optical fibers 101 between the substrates 102 with V-shaped grooves and between the uppermost substrate 102 with V-shaped grooves and the fixing member 103, and stacking the substrates in such a manner that a front surface of each substrate 102 with V-shaped grooves is brought into contact with a back surface of the adjacent substrate 102 with V-shaped groove (for example, JP-A-56-113114).
A waveguide substrate (unit) 205 having one or more waveguides 201 patterned near a surface thereof, shown in FIG. 17, has been used in a splitter, AWG or waveguide modulator, for example. FIG. 17(a) is a schematic plan view of a splitter with one channel input and eight channel outputs, and FIG. 17(b) is a cross-sectional view taken along a line Xxe2x80x94X in FIG. 17(a).
However, the conventional two-dimensional optical fiber arrays have problems as described below.
(1) It is difficult to control the thickness of a substrate having V-shaped grooves on a surface thereof (substrate with V-shaped grooves, simply referred to as a substrate occasionally hereinafter) with a precision of the order of submicrons, and the industrial limit of error for the entire surface of the substrate is approximately xc2x11 xcexcm. For example, if eight substrates each having a thickness error of +1 xcexcm are stacked, the resulting 2DFA has a thickness error of +7 xcexcm at the maximum. Thus, the alignment precision of the optical fibers is inevitably low.
(2) Since the substrates abut on each other, the thickness of an adhesive layer therebetween is substantially 0. This is unfavorable for adhesion for most adhesives. In particular, if the substrates abut on each other over the substantially entire surface, the long-term reliability thereof is not always sufficiently assured.
(3) In the case where the upper substrate of adjacent two substrates serves as a fixing member for the lower substrate, including the case where it serves as a lid, it is inevitably required to adopt a method of xe2x80x9coptical fiber array formation (FA formation) after stackingxe2x80x9d, in which the substrates are stacked and ferruled, and then the optical fibers are inserted, or a method of xe2x80x9cFA formation simultaneous with stackingxe2x80x9d, in which the optical fibers are placed in the V-shaped grooves of the lowermost substrate before the second lowest substrate is positioned and placed on the lowermost substrate, the optical fibers are placed in the V-shaped grooves of the second lowest substrate before the third lowest substrate is positioned and placed on the second lowest substrate, and such a process is successively carried out. In the case of the former method of xe2x80x9cFA formation after stacking,xe2x80x9d in order to assure precision, a hole, into which the optical fiber is to be inserted, has to be designed to minimize a clearance from the optical fiber. Thus, the hole is so small that it is extremely difficult to assemble the optical fibers without cutting. For example, in the case of the 2DFA comprising eight stacked substrates each having eight optical fibers aligned thereon, the number of optical fibers to be inserted is 64. Also in the case of the latter method of xe2x80x9cFA formation simultaneous with stackingxe2x80x9d, the process is complicated and it is difficult to assemble the optical fibers without cutting. In addition, it is extremely difficult to simultaneously conduct positioning of the substrate and alignment of optical axes in each substrate including parallelization.
(4) In order to solve the above problem (3), there has been proposed an optical fiber array having, between the substrates with V-shaped grooves stacked one on another, an accommodation section for accommodating an optical fiber presser member (equivalent to the fixing member in this invention) in a state where the tops of the optical fibers protrude slightly from the V-shaped grooves and the optical fiber presser member on one substrate is kept from contact with the other substrate with V-shaped grooves (Japanese Patent No. 3108241). This optical fiber array is superior in that it has enhanced workability and alignment precision because a procedure of stacking after FA formation can be adopted. However, the above-described problems (1) and (2) associated with the alignment precision and the long-term reliability, respectively, has not been solved yet.
(5) As another approach for solving the above problem (3), there has been proposed an optical fiber multicore connector having a groove for an optical fiber and a rod for aligning axes of connector terminals (JP-A-55-45051). With the optical fiber multicore connector, although the procedure of FA formation simultaneous with stacking is involved, the workability is enhanced because the positioning is accomplished automatically by the action of the V-shaped grooves and the optical fibers. And, the above problem (2) of the long-term reliability can be solved depending on the setting of the depth of the groove. However, the above problem (1) of the alignment precision remains, and it is difficult to align the V-shaped grooves on both surfaces of a substrate with those on another substrate in the width direction. Thus, an additional problem of misalignment in the width direction has arisen.
(6) An optical communication network involving the two-dimensional optical fiber arrays described above has various connection points therein. The connection points each reflect light passing therethrough, and when the reflected light is launched again into its original fiber, a laser or the like is disadvantageously affected (a noise occurs, for example). In particular, in the case of the 2DFA mainly used for the MEMS switch or the like, since lens coupling is often adopted, and a space is provided immediately after the 2DFA, the reflected light, which is launched into the original fiber again, has a significant influence.
(7) To eliminate the disadvantage described above, in the past, reflection from an end face has been suppressed by providing an AR coating (which is formed by stacking an SiO2 film and a TiO2 film each having a thickness of xc2xcxcex and has a total thickness of the order of a wavelength of light (xcex)) on the substrate and a light-emitting end face of the optical element, thereby enhancing reflection characteristics at the end faces. However, the AR coating film is easily degraded by effects of temperature, humidity and other environmental factors and adversely affects the reflection characteristics. Recently, in particular, with the development of the wavelength division multiplex (WDM) communication, the quantity of light transmitted through one optical fiber has been increased, and accordingly, the possibility of a local change in characteristics or local degradation due to the increased quantity of light (light with increased intensity) has been increased. Besides, since the AR coating is provided on the end face of the fiber array when the fibers are mounted thereon, it is difficult to use vacuum processing for vapor deposition of the AR coating. Thus, multiple AR coatings cannot be conducted at a time, and the cost is increased.
In addition, the above-described waveguide substrate has a problem as follows. When connecting the waveguide substrates and the optical fiber arrays with each other, each of the optical fiber arrays needs to be optically aligned with one of the waveguide substrates. In this alignment, the waveguide substrate and the optical fiber array are aligned with each other on the level of submicrons, and thus, the alignment inevitably requires extremely high precision and many process steps.
The present invention has been devised in view of the above-describe problems, and an object of this invention is to provide a two-dimensional optical element array with a high alignment precision of optical elements (optical fiber, lens, for example) on a substrate and a high long-term reliability, and a two-dimensional waveguide apparatus having high density and capacity and allowing the number of steps in packaging or connection to be reduced.
After earnest research, the inventor has found that the above problems can be solved by stacking a plurality of optical element array units, each of which is a set of a substrate and one or more optical elements aligned and fixed in the grooves thereof, in such a manner that surfaces of the substrates of adjacent optical element array units, which face to each other, are kept from direct contact with each other and from having a direct mechanical influence on each other (the same applies to a plurality of waveguide substrate units each having one or more waveguides patterned thereon in a planar manner). Thus, this invention has been completed.
Specifically, this invention provides a two-dimensional optical element array and a two-dimensional waveguide substrate apparatus as described below.
First there is provided a two-dimensional optical element array, which includes a stack of a plurality of optical element array units each having an optical element and a substrate, the substrate has one or more grooves, each suited to a profile of the optical element on one of surfaces thereof, and one or more optical elements being aligned and fixed in the grooves. The plurality of optical element array units are stacked in a state such that surfaces of the substrates among adjacent two units facing each other do not directly contact each other, and the adjacent two units do not have a direct mechanical influence on each other. Here, xe2x80x9cthe state the adjacent two units do not have a direct mechanical influence on each otherxe2x80x9d means xe2x80x9cthe state that a force, vibration or the like is not directly transmitted among the adjacent two units,xe2x80x9d and the same applies to the following description.
It is preferable that the optical element in the two-dimensional optical element array is an optical fiber or lens.
It is preferable that an apex of an optical element arranged on a substrate of a first optical element array unit is brought into contact with a surface of a substrate of a second optical element array unit, both of which face each other. Further, that the surfaces of the substrates of adjacent two optical element array units do not directly contact each other, and that the adjacent two units do not have a direct mechanical influence on each other in the two-dimensional optical element array.
It is preferred to stack the plurality of optical element array units in such a manner that an adhesive layer is interposed between an apex of an optical element arranged on the substrate of a first optical element array unit and a surface of a substrate of a second optical element array unit both of which face each other. Additionally, the apex of an optical element arranged on a substrate of a first optical element array unit is brought into contact with a surface of a substrate of a second optical element array unit. Both substrates of first and second units face each other, but the surfaces of the substrates of adjacent two optical element array units do not directly contact each other, and the adjacent two units do not have a direct mechanical influence on each other in the two-dimensional optical element array.
According to the present invention, there is also provided a two-dimensional optical element array, which further includes a fixing member on one of the surfaces of the substrate of the uppermost optical element array unit and between the substrates of adjacent optical element array units. The fixing member presses or mounts the optical element against or on one surface with the grooves of the substrate for alignment and fixing.
Further provided is a two-dimensional optical element array in which the fixing member presses or mounts the optical element against or onto the surface with the grooves of the substrate for alignment and fixing in such a manner that a surface of the fixing member and a surface of the substrate of the optical element array unit which faces the surface of the fixing member do not directly contact each other, and that the adjacent two units do not have a direct mechanical influence on each other.
Further provided is a two-dimensional optical element array of which optical element is pressed against or mounted on the substrate for alignment and fixing in such a manner that the optical element abuts on a surface of the fixing member and on a side wall of the groove(s).
It is also preferable that the optical element array unit(s) further include an adhesive layer disposed between the surface of the fixing member and the surface of the substrate of the optical element array unit which faces the surface of the fixing member.
It is also preferable that a thickness of the adhesive layer falls within a range from 2 to 100 xcexcm.
It is also preferable to form a positioning guide at a predetermined position on the surface with the grooves of the substrate of the optical element array unit.
It is also preferable that the groove is a V-shaped groove.
It is preferable to slant a light-emitting end face and/or light receiving end face of the optical element of the optical element array unit by a predetermined angle (xcex8) with respect to a plane perpendicular to a central axis of the optical element.
It is also preferable to dispose the light-emitting end face and/or light receiving end face of the optical element in the plane perpendicular to the central axis of the optical element.
It is also preferable to dispose the light-emitting end face and/or light receiving end face of the optical element in a plane angled by a predetermined angle (xcex8) with respect to the plane perpendicular to the central axis of the optical element.
It is also preferable to dispose the light-emitting end face and/or light receiving end face of the optical element in a plane perpendicular to an optical axis of an emitted light and/or incident light, respectively.
According to the present invention, it is further provided with a method of measuring a core position of an optical element of the two-dimensional optical element array which comprises the steps of:
a) Measuring core positions of m rows of optical elements and measuring core positions of at least two of n columns of optical elements, in the case where m optical element array units are stacked and each optical element array unit has n channels (in the case where the optical elements are arranged in m rows and n columns).
b) Arbitrarily designating one optical element for each of the at least two columns of optical elements and measuring a distance D between the core positions of the optical elements designated (designated optical elements).
c) Calculating a positional relation among elements of a matrix of the core positions of the optical elements at four corners of a rectangular having a line segment connecting the core positions of the designated optical elements as a diagonal line thereof and calculating the core positions of all of the optical elements.
According to the present invention, there is further provided a two-dimensional waveguide apparatus, which includes a stack of a plurality of waveguide substrate units each having one or more waveguides patterned in a planar manner. The plurality of waveguide substrate units are stacked in a state such that the surfaces of the substrates of two adjacent waveguide substrates do not directly contact each other, and that the two adjacent units do not have a direct mechanical influence on each other.
There is further provided a two-dimensional waveguide apparatus which further includes an adhesive layer between the surfaces of two adjacent waveguide substrate units that face each other.
It is preferable that a thickness of the adhesive layer falls within a range from 2 to 100 xcexcm.
It is also preferable to form a positioning guide at a predetermined location on a surface of the waveguide substrate unit.
It is also preferable to slant a light-emitting end face of each waveguide of the waveguide substrate unit by a predetermined angle (xcex8) with respect to a plane perpendicular to an optical axis thereof.
There is further provided a two-dimensional waveguide apparatus, in which the light-emitting end face and/or light receiving end face of the waveguide of the waveguide substrate unit is disposed in a plane perpendicular to a central axis of the waveguide.
There is also provided a two-dimensional waveguide apparatus in which the light-emitting end face and/or light receiving end face of the waveguide of the waveguide substrate unit is disposed in a plane angled by a predetermined angle (xcex8) with respect to the plane perpendicular to the central axis of the waveguide.
There is also provided a two-dimensional waveguide apparatus in which the light-emitting end face and/or light receiving end face of the waveguide of the waveguide substrate unit is disposed in a plane perpendicular to an optical axis of an emitted light and/or incident light, respectively.